For example, the patent application DE 10 2013 218 401 A1 is known from the prior art. Said document concerns a method for the operation of a motor vehicle, wherein at least one autonomous or partially autonomous mode of the motor vehicle can be activated and the motor vehicle comprises an operating brake and a parking brake, characterized in that in response to a recognized operating state of the motor vehicle the parking brake is changed from a rest state to a predetermined operating state, wherein the predetermined operating state of the parking brake is determined such that the parking brake produces no braking effect or produces a braking effect that is significantly lower compared to full activation.
Parking brakes are adjusted when released, i.e. disengaged, such that there is no reaction of the parking brake on the operating brake system. In order to achieve this, the following requirements must be taken into account:
(1) A reduction of force occurs,
(2) the air gap must be opened (this is set by the seals of the brake piston; the brake piston is retracted slightly into the brake caliper for this)
(3) other effects, such as for example imbalance of the brake disk/disk run-out should not result in a brake torque and
(4) a safety margin is provided by which the parking brake mechanism is opened further. Said distances must be overcome when next re-engaging. In particular, the distances (2) through
(5), which define the entire force-free region. In relation to the overall application when engaging, approximately ½ to ⅔ of the entire activation time is required for this.
Furthermore, systems are known that enable partially automatic or fully automatic parking. Here, following the completion of the parking process, there is generally a change from holding hydraulically to holding (electro)mechanically. The handover from hydraulic holding to (electro)mechanical holding is relatively slow. The activation sequence, i.e. the required activation time, for automated electromechanical parking brakes generally requires 1 to 1.5 seconds. Said time is a function of the entire system, the setting position of the free travel (i.e. the actuator position in the disengaged state) and the voltage level. Until the parking brake is effective fully and to the required extent, hydraulic holding must be used. Otherwise there is a risk that the vehicle may roll away in the event of there being a suitable upslope or downslope. The feedback to the driver is therefor made with a suitable time delay.